Suppose that you contract a loan of 8,000 Ethurum, and you opt to repay it using a 12-month payment plan for n years. In this plan, you make monthly payments of 215.67 Ethurum each, with the first payment due one month after receiving the loan. Interestingly, if you were to make 12n monthly payments of 210.80 Ethurum each at the same interest rate, the total accumulated amount would be 12,500 Ethurum, one month after the final payment. Calculate the equivalent effective annual interest rate for this loan situation.